🩺 Acute Limb Weakness

Acute limb weakness represents a neurological emergency until proven otherwise. It can arise from pathology anywhere in the motor system, including the motor cortex, spinal cord, peripheral nerves, neuromuscular junction, or muscles. The primary goal is to differentiate life-threatening or disabling conditions like acute stroke and spinal cord compression from peripheral neuropathies. Rapid assessment and imaging are crucial for interventions such as thrombolysis or surgical decompression. The presentation may involve a single limb or multiple limbs, often accompanied by sensory or autonomic changes.

Duration and speed of onset are critical: sudden onset suggests vascular (stroke) or mechanical (cord compression), while subacute suggests inflammatory (GBS) or infective causes. Determine the distribution: Is it a single limb (monoplegia), one side of the body (hemiplegia), both legs (paraplegia), or all four (tetraplegia)? Ask about sensory changes, back pain, and autonomic dysfunction (bladder/bowel). Screen for recent infections (common in GBS) or a history of malignancy (spinal cord compression). Enquire about risk factors for stroke, such as atrial fibrillation, hypertension, and smoking.

Perform a structured neurological exam: assess tone, power (using the MRC scale 0-5), reflexes, and sensation. Upper Motor Neuron (UMN) signs (hyperreflexia, extensor plantars, spasticity) suggest a central cause (brain/cord). Lower Motor Neuron (LMN) signs (hyporeflexia, wasting, fasciculations) suggest peripheral nerve, plexus, or root pathology. In spinal cord presentations, identify a 'sensory level' to localise the lesion. Perform a PR exam to assess anal tone if Cauda Equina is suspected. Screen for cranial nerve involvement which may suggest a brainstem stroke or GBS variant (Miller Fisher).

Ischaemic or Haemorrhagic Stroke, Spinal Cord Compression (e.g., malignancy, abscess), Cauda Equina Syndrome, Guillain-Barré Syndrome (GBS), Multiple Sclerosis (Relapse), Todd's Paralysis (post-seizure), Myasthenia Gravis, Electrolyte imbalance (e.g., hypokalaemia), Acute Limb Ischaemia.

Sudden onset 'worst ever' headache or visual loss (Stroke), Urinary retention or faecal incontinence (Cauda Equina), Rapidly ascending weakness (GBS/Respiratory failure), Saddle anaesthesia, History of trauma or known malignancy, Fever with back pain (Spinal abscess).

Urgent neuroimaging is the priority. For suspected stroke, a non-contrast CT Head is performed to rule out haemorrhage before thrombolysis. For suspected spinal cord compression or Cauda Equina, an urgent MRI Spine is mandatory. If Guillain-Barré is suspected, lumbar puncture (showing albuminocytological dissociation—high protein, low/normal cells) and nerve conduction studies are indicated. Routine labs should include FBC, Clotting, Glucose, and INR. If a metabolic cause is suspected, check U&Es (hypokalaemia/hyperkalaemia) and CK (rhabdomyolysis).

Time is brain; if a stroke is suspected, 'Face Arm Speech Test' (FAST) positivity should trigger immediate transfer to a hyperacute stroke unit. Remember that 'Saddle Anaesthesia' or bladder/bowel dysfunction makes Cauda Equina Syndrome an emergency requiring immediate MRI and surgical consultation. In Guillain-Barré, the weakness is typically ascending and may involve the muscles of respiration; monitoring Vital Capacity (VC) is more important than oxygen saturations in these patients. In cases of sudden monoplegia with sensory loss, consider an arterial embolus (the '6 Ps' of limb ischaemia) as a mimic of neurological weakness.

Relevant to 'Stroke Medicine', 'Emergency Medicine', and 'Neurology'. Students must distinguish between UMN and LMN lesions and know the immediate management of acute stroke (thrombolysis window usually <4.5h) and MSCC (dexamethasone and urgent MRI/referral).